An electron and a proton are separated by a distance of 1 m. What happens to the size of the force on the first electron if a second electron is placed next to the proton?

The force on the electron will become zero.

Explanation:

As electron has negative charge and proton has positive charge. The magnitude of charge on both particles is equal. Therefore, there will be a force of attraction between electron and proton. When another electron is brought near the proton the net charge in that area will become equal to zero. Therefore, first electron will not experience any force.